The present invention relates to four-color halftone printing onto objects having a curved surface, and more particularly to a process for conducting four-color halftone printing onto cylindrical, conical and elliptical objects by means of a dry offset printing process and a curved surface printing machine used therefor by means of a dry offset printing.
Printing of cylindrical metallic cans and tubes is usually conducted by a dry offset printing process, and a four-color tube printing machine is widely employed for multicolor printing at the present time. In the printing using such a printing machine, halftone images of four colors are first transferred onto the same position on a blanket in order from each block supported on four block cylinders arranged around a blanket cylinder, and then transferred from the blanket onto a can or tube which is set to a mandrel provided on a rotating disc and is rotatable in contact with the blanket by the rotation of the blanket cylinder. However, such a known tube printing process has the disadvantage that when patterns transferred onto the blanket from blocks overlap each other, the inks in a wet state draw each other and are mixed together, and as a result, the hue changes into an entirely different one. Therefore, it is very difficult to conduct three-color or four-color halftone printing to reproduce the same color as the original, and a conventional tube printing has been limited in design.